Process for enhanced total organic carbon removal while maintaining optimum membrane filter performance

ABSTRACT

A system and process for enhancing total organic carbon (“TOC”) removal from raw, untreated water while maintaining optimum membrane filter performance. The present invention overcomes many of the disadvantages of prior art water filtration systems by controlling the pH level of the water, prior to the water being directed through said membrane filter, so that the particulate charge of the water aligns with the electromagnetic surface charge of membrane filter. Maintaining the particulate charge of the water within an optimum charge window for the particular membrane filter enhances the membrane filter&#39;s performance by decreasing the fouling rate of the membrane filter.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 11/975,835, filed Oct. 23, 2007, and claims benefit of priorityto U.S. Provisional Patent Application No. 61/196,918, filed Oct. 22,2008. The technical disclosures of these documents are incorporatedherein in their entirety by reference.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The present invention relates to a process for enhancing the removal oftotal organic carbon from a water supply while optimizing theperformance of a membrane filtration system.

2. Description of Related Art

Increasingly, municipal drinking water and wastewater filtrationfacilities utilize membrane microfiltration or ultrafiltration systemsas a means of filtering ground water, surface water and wastewatersources (“source water”). Such filtration systems typically utilize asemi-permeable membrane device to filter or reject organic, inorganicand microscopic particulates as water is passed through them. As sourcewater is passed through the membrane filter barrier under hydrostaticpressure, particulate debris (i.e., suspended solids and solutes of highmolecular weight) accumulates on the membrane surface and is retained orfiltered from the water, while water and low molecular weight solutespass through the membrane. Typically, insoluble particulates sizedlarger than 0.04-0.1 microns are filtered or rejected while solublecontaminants or insoluble particulates and ions less than 0.04-0.1microns pass through the membrane filter.

To function efficiently, it is important that the membrane filter iskept clean. The membrane is, therefore, periodically backwashed toremove the particulate buildup. Accumulated particulates that are notreadily removed during backwashing must be removed by chemical cleaningtechniques. Such techniques, commonly known as clean in place (CIP)and/or chemical maintenance wash procedures, involve exposing themembrane to chemicals such as caustic soda, sodium hypochlorite(chlorine), various acids and other chemical products to remove thebuild-up of organic and inorganic compounds. However, chemical cleaningtechniques are much more time consuming when compared to backwashingalone. Moreover, the harsh chemicals used in chemical cleaningtechniques tend to degrade and deteriorate the membrane filter elementover time.

The performance of a filtration membrane is dictated by the fouling rateof the influent contaminants. Fouling is the buildup of organic andinorganic particulates on the membrane surface that are not readilyremoved during periodic backwashing. As the fouling rate of a membranefilter element increases, chemical maintenance wash procedures are morefrequently required. Most membrane filtration systems operate withoutany additional cleaning processes or chemical treatment past thebackwashing and chemical cleaning as described in the above paragraph.Thus, in order to optimize the performance of a filtration membrane itis desirable to minimize the fouling rate of the filtration membrane.

One type of contaminant in water supplies that increases the foulingrate of filtration membranes is total organic carbon (“TOC”). TOC levelsvary in water supplies from very pristine (i.e., low levels of TOC) tovery contaminated (i.e., high levels of TOC). Higher levels of TOCcontribute to taste and odor problems and the formation of disinfectionbyproducts (“DBP”) such as halo-acetic acid (“HAA”) and total tri-halomethane (“TTHM”). HAAs and TTHMs are created when chlorine reacts withsoluble organics and are typically formed when chlorine in the waterreacts with soluble TOC in the water distribution system (e.g., acollection of pipes that delivers filtered water to homes andbusinesses). Reducing the level of TOC, particularly the soluble TOC, inthe raw water alleviates the taste and odor problems and minimizes theformation of DBPs.

TOC consists of both soluble and insoluble compounds. However, membranefiltration alone only removes the insoluble component of TOC. A commonmethod for removing the soluble component of TOC includes introducing achemical coagulant into the water stream and providing adequate mixingand detention prior to membrane filtration. Metal salt-based coagulantsreact with soluble organics via a process known as “chargeneutralization,” which causes a portion of the soluble organic compoundsto precipitate out of solution thereby allowing them to be filtered outof the water. The metal base of these coagulants is generally aluminumor iron. Several chemical coagulants can provide this chemical reaction,such as aluminum sulfate, ferric chloride, ferric sulfate, poly-aluminumchloride and aluminum chlorhydrate.

The removal of TOC by coagulants can be further increased by adjustingthe pH of the water. Generally, the lower the pH, the greater the TOCremoval. For example, when a coagulant is dosed into a water stream, andthe pH is depressed chemically to a desired level and maintained(example: pH≈5.5), a higher level of TOC removal can be achieved.

Prior art methods have previously assumed that the pH set point foroptimal organic removal is the same for optimum membrane performance,but this is not necessarily true. Optimum membrane performance can bedefined as continuous filtration with 1) the lowest pressure rise acrossthe membrane, measured as trans-membrane pressure (TMP); and 2) thelowest chemical cleaning requirement.

The trans-membrane pressure (TMP) is generally a function of the forcewhich drives liquid flow through a cross flow membrane (TMP={(feedpressure+retentate pressure)/2}−permeate pressure), whereas the lowestchemical cleaning requirement is a simply a function of minimizing thefouling rate of the membrane. During filtration, the feed side of themembrane is under higher pressure than the permeate side. This pressuredifference forces liquid through the membrane. Consequently, rising TMPis an indicator of membrane fouling.

Prior art methods to remove TOC include 1) installing a process aftermembrane filtration such as granular activated carbon (GAC) adsorption,2) dosing a chemical coagulant prior to membrane filtration withoutcontrolling pH, 3) only controlling pH ahead of a liquids-solidsseparator prior to membrane filtration, 4) only controlling pH fororganic removal, 5) installing an ion exchange process before membranefiltration, or 6) installing a nano filtration or reverse osmosisprocess after membrane filtration. Thus, an improved process for waterfiltration, which enhances TOC removal while optimizing membrane filterperformance, is desirable.

SUMMARY OF THE INVENTION

The present invention involves a system and process for enhancing totalorganic carbon (“TOC”) removal from raw, untreated water whilemaintaining optimum membrane filter performance. The present inventionovercomes many of the disadvantages of prior art water filtrationsystems by controlling the electromagnetic particulate charge in orderto enhance membrane filter performance by decreasing the fouling rate ofthe membrane.

Fouling is the buildup of organic and inorganic particulates on themembrane surface that are not readily removed during periodicbackwashing. It has been found that these particulates, as well as themembrane surface, possess a micro amp charge. When the electromagneticcharge of the particulates aligns with electromagnetic charge of themembrane surface, there is no electromagnetic attraction and thefiltered particulates are easily removed from the membrane surfaceduring backwashing. However, when the electromagnetic charge of theparticulates does not align with the membrane surface charge, theparticulates are attracted to the membrane surface and not readilyremoved by backwashing, resulting in fouling of the membrane. The rateof fouling can be attributed to the difference in charge between theparticulate and the membrane surface. By adjusting the pH of the water,the electromagnetic charge of these particulates may be altered and madeto align with the membrane surface charge, thereby reducing fouling ofthe membrane and improving the membrane's performance.

In one embodiment, the system comprises a two-stage process in which theelectromagnetic particulate charge of the water is controlled in thesecond stage by adjusting the amount of acid or base added to the waterprior to membrane filtration. In the first stage of the process, acoagulant is dosed and the pH of the water is controlled in order toachieve maximum TOC removal during liquids-solids filtration. Utilizingthis two-stage process allows the total system to operate moreeffectively and further achieves maximum TOC removal and optimummembrane performance.

In a second embodiment, the system of the present invention comprises asingle stage or direct feed mode wherein the pH/electromagnetic chargelevel is controlled so that water dosed with a coagulant may bypass aclarifier and proceeds directly to the membrane filtration system. In adirect feed mode, coagulant is dosed ahead of a mixing system. The pHand electromagnetic particulate charge of the water may be controlled bymeans of pH control, micro amp streaming current control, pH controlwith temperature correction and/or TMP/Resistance/Permeability control.Any one or a combination of these control mechanisms may be utilized tomaintain an optimum set point by adjusting the acid or base dosinglevels. In general, the pH and electromagnetic particulate charge of thewater are maintained at levels that achieve as much TOC removal aspossible while optimizing membrane performance.

The filtration system of the present invention may further include acomputerized master control system, which continually monitors thefiltration system and automatically adjusts the acid and base dosinglevels and the amount of coagulants added to the water based on a numberof criteria. The master control system allow the filtration system to befine tuned during operation so as to enhance the total organic carbon(“TOC”) removal from raw, untreated water while maintaining optimummembrane filter performance

The above as well as additional features and advantages of the presentinvention will become apparent in the following written detaileddescription.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the invention are setforth in the appended claims. The invention itself, however, as well asa preferred mode of use, further objectives and advantages thereof, willbe best understood by reference to the following detailed description ofillustrative embodiments when read in conjunction with the accompanyingdrawings, wherein:

FIG. 1 is a schematic diagram of a first embodiment of the membranefiltration system of the present invention;

FIG. 2 is a schematic diagram of a second embodiment of the membranefiltration system of the present invention; and

FIG. 3 is a schematic diagram of the master control panel of themembrane filtration system of the present invention.

Where used in the various figures of the drawing, the same numeralsdesignate the same or similar parts. Furthermore, when the terms “top,”“bottom,” “first,” “second,” “upper,” “lower,” “end,” “side,”“horizontal,” “vertical,” and similar terms are used herein, it shouldbe understood that these terms have reference only to the structureshown in the drawing and are utilized only to facilitate describing theinvention.

All figures are drawn for ease of explanation of the basic teachings ofthe present invention only; the extensions of the figures with respectto number, position, relationship, and dimensions of the parts to formthe preferred embodiment will be explained or will be within the skillof the art after the following teachings of the present invention havebeen read and understood. Further, the exact dimensions and dimensionalproportions to conform to specific force, weight, strength, and similarrequirements will likewise be within the skill of the art after thefollowing teachings of the present invention have been read andunderstood.

DETAILED DESCRIPTION OF THE INVENTION

The present invention comprises a process and system for enhancing totalorganic carbon (“TOC”) removal from raw, untreated water whilemaintaining optimum membrane filter performance. The present inventionenhances membrane filter performance by decreasing the fouling rate ofthe membrane filter.

Fouling is the buildup of organic and inorganic particulates oil themembrane surface that are not readily removed during periodicbackwashing. It has been found that low pressure membrane fouling can becaused by organic and inorganic particulates coming into contact withthe membrane surface. It has been determined that these particulates, aswell as the membrane surface, possess a micro amp charge. It has beenfurther determined that the micro amp charge of particulates does notalways align with the natural surface charge of the membrane surface.

While the surface charge of the filtration membrane is fairly constant,the electromagnetic particulate charge is more variable depending onfactors such as coagulant dose, pH changes, temperature, particle size,etc. It is, therefore, important to control or “align” the particulatecharge with the membrane surface charge. By “align” is meant controllingthe particulate charge so that it matches the membrane surface charge.In accordance with the system and process of the present invention, thisaligning is accomplished by controlling the acid or base feed tomaintain the desired particulate charge so that it matches the surfacecharge of the membrane. When the electromagnetic particulate chargealigns with the membrane surface charge, electromagnetic attraction isceased, and the filtered particulates are easily removed from themembrane surface during backwashing. However, when the electromagneticparticulate charge does not align with the membrane surface charge, theparticulates are attracted to the membrane surface and fouling occurs.

The rate of fouling can be attributed to the difference inelectromagnetic charge between the particulates and the membranesurface. By adjusting the pH of the water, the electromagnetic charge ofthese particulates may be altered and made to align with theelectromagnetic charge of the membrane surface, thereby reducing foulingof the membrane and improving the membrane's performance.

In accordance with the process and system of the present invention, theparticulate charge is controlled such that the micro amp charge of theparticulates aligns with the membrane surface charge, thereby allowingthe filtered particulates to be easily removed from the membrane surfaceduring backwashing.

For example, with reference to FIG. 1, a first embodiment of a membranefiltration system of the present invention is depicted. As shown in FIG.1, the membrane filtration system comprises a two-stage system, whichenhances the total organic carbon (“TOC”) removal from raw, untreatedsource water while maintaining optimum membrane filter performance.

In the first stage, a stream of raw untreated source water 10 isdirected into a first or primary mixing tank 14 where it is dosed with acoagulant and the pH of the water is controlled such that a maximumlevel of TOC is removed during liquids-solids separation. When thecoagulant is completely blended and the pH of the water is stabilized,the first stage water flows from the primary mixing tank 14 and passesthrough a mechanical clarifier 28. The clarifier 28, or liquids-solidsseparator, separates the chemically flocculated particulates from thewater and removes them from the system. It is in this unit thatchemically precipitated TOC removal occurs.

In the second stage, the particulate charge of the water is controlledto achieve optimum membrane filter performance. The first stage waterflows from the clarifier 28 and is introduced into a secondary mixingtank 30. In the secondary mixing tank 30, the particulate charge of thewater is monitored and the appropriate amount of acid or base is addedto water to maintain an optimum charge window which matches theelectromagnetic charge of the membrane surface. The optimum chargewindow, which is typically in the low anionic (−) range, is chosen toalign with the natural surface charge of the membrane in order to reducefouling. Thus, the electromagnetic charge of the membrane filter dependson the type of filter used. The particulate electrical charge can alsobe affected by factors such as turbidity increase/decrease, temperature,conductivity and the type of particulates in the water. When theparticulate charge of the water is stabilized, the water flows from thesecondary mixing tank 30 and passes through a low pressure membranefilter 50. The membrane filter 50 removes particulates from the waterthat are larger than the membrane's pore size.

In addition, the pH of the water, trans-membrane pressure (“TMP”),membrane resistance, and membrane permeability may also be monitored toprevent runaway chemical dosing. The membrane filtration system providesthe final process step before the water is disinfected prior todistribution to homes and businesses. The filtered water is typicallystored in a clear well into which chlorine is dosed to preventbiological growth in the water in the distribution system. Utilizingthis two-stage process allows the entire filtration system to operatemore effectively.

With reference again to FIG. 1, the first embodiment of the membranefiltration system of the present invention will be described in greaterdetail. The stream of raw untreated source water 10 is directed into aprimary mixing tank 14, which is preferably a steel, fiberglass orconcrete vessel. The source water 10 is then dosed with an effectiveamount of coagulant based upon a variety of factors such as volume, TOClevel, distribution system detention and temperature.

For example, the system may include a flow meter 12, which monitors thevolume of water entering the primary mixing tank 14. The system may alsoinclude a TOC analyzer 62 and UV 254 analyzer 64, which further monitorthe water in the primary mixing tank 14. The TOC analyzer 62 determinesthe amount of TOC in the water. The UV 254 analyzer 64 provides ameasurement of the portion of TOC that is most reactive to chlorine andresults in the formation of disinfection byproducts (“DBP”). Bothanalyzers pull water from the primary mixing tank 14, filter the waterand provide measurements that simulate the process of coagulation, pHadjustment and filtration. In short, the measurements are a simulationof the water that will be entering the distribution system.

A temperature sensor 44 monitors the temperature of the water in thesystem. While the temperature sensor 44 is shown to measure thetemperature of the water in a secondary mixing tank 30 in FIG. 1, it isunderstood that temperature sensor 44 may comprise one or moretemperature monitors located at different positions in the system. Forexample, temperature sensor 44 may be positioned the point of dischargefrom the water treatment system, the point of entry to the watertreatment system, or in the primary mixing tank 14. The temperature ofthe water is an important variable to consider in determining thecoagulant and chlorine dose since the reaction between organics andchlorine increases as the temperature increases, forming moredisinfection byproducts (“DBPs”) in the water.

Based upon an analysis of the variety of factors (e.g., flow volume, TOClevel, and temperature), the source water 10 is then dosed with aneffective amount of coagulant. As used herein, an “effective amount” ofcoagulant means an amount sufficient to cause precipitation of solubleTOC particulates in the water. Laboratory simulation utilizing an actualwater sample can determine the amount of coagulant and pH levelnecessary to achieve the desired precipitation of soluble organiccompounds (expressed as the % TOC removal required). For example, awater treatment plant determines through laboratory testing that atarget of 40% soluble TOC removal will reduce DBP formation withinlimits to comply with federal limits (Stage 1 and Stage 2 DBP Rule). Aneffective amount of coagulant typically ranges from 1 part per million(“ppm”) to 50 ppm, but may be as high as 250 ppm. A higher dose ofcoagulant generally results in higher TOC removal, but there is athreshold beyond which TOC removal ceases regardless of the dosage.Examples of coagulants that may be used include aluminum sulfate,polyaluminum chloride, aluminum chlorhydrate, ferric sulfate, and ferricchloride.

In a preferred embodiment, the filtration system depicted in FIG. 1further includes a master control panel 60, which collects and analyzesinputs from the flow meter 12, TOC analyzer 62 and UV 254 analyzer 64,to determine an effective amount of coagulant to be added to the waterin the primary mixing tank 14. Measurement data from the flow meter 12,TOC analyzer 62 and UV 254 analyzer 64 are typically sent to the mastercontrol panel 60 by means of wireless or hardwire electronic signalcommunications. Based upon input data from the flow meter 12, thetemperature sensor 44, the TOC analyzer 62, and the UV 254 analyzer 64,the master control panel 60 uses a programmed algorithm to calculate aneffective amount of coagulant to be added to the water in the primarymixing tank 14. The master control panel 60 then sends an electronicsignal to coagulant dosing system 16 to dose an effective amount ofcoagulant into the primary mixing tank 14. Alternatively, the coagulantcould be dosed further upstream of the primary mixing tank 14. Usingthis automated system for coagulant dosing provides for an accuratemetering of coagulant, lowers the amount of coagulant required, andreduces operating costs by avoiding coagulant overdoses.

The pH of the water in primary mixing tank 14 is also monitored. Basedupon an analysis of the pH and TOC level, an appropriate amount of acidor base is added to the water in order to enhance the precipitation ofTOC from the source water.

In a preferred embodiment, the system includes a pH probe 26, whichsends an electronic signal to the master control panel 60. The mastercontrol panel 60 uses the input data from the pH probe 26, the TOCanalyzer 62 and the UV 254 analyzer 64 to calculate the appropriateamount of acid or base to add to the water in the primary mixing tank14.

In accordance with the process of the present invention, the water inthe primary mixing tank 14 is typically dosed with acid or base tomaintain a pH or 4.0 to 6.0 standard units. Suppressing the pH of thewater results in higher TOC removal because soluble TOC removaltypically increases as pH is depressed. The value of pH has a profoundeffect in flocculation because it changes the ionic character of theorganics. The charge of the organics changes in response to theconcentration of positively charged hydrogen ions and negatively chargedhydroxyl ions which surround them. Organics in water become morenegatively charged (i.e., “anionic”) as pH is increased and morepositively charged (i.e., “cationic”) as pH is decreased. Therefore,organic removal increases as the pH is depressed.

For example, if source water containing organics is dosed with acoagulant (acidic/cationic) at 20 ppm, X amount offlocculation/precipitation is achieved. However, if the source water isfirst dosed with the coagulant (acidic/cationic) at 20 ppm and then thepH of the water is depressed with an acid, higher amounts offlocculation/precipitation (e.g., X+m) can be achieved. Theconcentration of hydroxyl ions, which are surrounding them and theflocculated particle (precipitated metal/salt acidic coagulant), carriesa positive charge, becomes more effective. Generally, soluble TOCremoval increases incrementally as the pH is suppressed. However, thereis a threshold beyond which TOC removal ceases regardless of pHsuppression. For example, when aluminum based coagulants are used, TOCremoval levels out at a pH of about 5.0 standard units, and when ironbased coagulants are used, TOC removal levels out at a pH of about 4.0standard units.

The master control panel 60 then sends an electronic signal to theprimary acid/base dosing system 18 to dose the appropriate amount ofacid or base into the primary mixing tank 14. Because the desired pH islow in this stage, the primary acid/base dosing system 18 will generallybe required to dose an acid into the primary mixing tank 14. Examples ofacids that may be used are sulfuric acid or phosphoric acid.

The water, coagulant and acid or base are then mixed in the primarymixing tank 14. The primary mixing tank 14 may comprise a single mixingzone with a single mixer 20, as shown in FIG. 1, or multiple mixingzones with multiple mixers 22, 24, as shown in FIG. 2. It is alsopossible to utilize the mixer in the riser tube of a solids contactclarifier thus reducing the requirement for the primary mixing system.This description demonstrates the requirement for mixing and detention.The author recognizes that there are alternate ways to achieve thiswithout the need for this mixing tank. The mixers are preferablyvertically mounted, propeller-type agitators. Referring to FIG. 2, whenmultiple mixing zones are utilized, the first zone contains a rapidmixer 22, which rapidly mixes the water to quickly disperse thecoagulant, and the second zone containing a slower speed flocculation ormaturation mixer 24, which promotes the flocculation of chemicallyprecipitated particulates. The water remains in the primary mixing tank14 for a sufficient time to completely blend the coagulant into thewater and for the pH to stabilize at the desired point. Typicaldetention times in the primary mixing tank 14 range from 1 minute to 30minutes.

Referring now to FIG. 1, when the coagulant is completely blended andthe pH of the water is stabilized, the first stage water flows from theprimary mixing tank 14 and passes through a mechanical clarifier 28. Theclarifier 28, or liquids-solids separator, separates the chemicallyflocculated particulates from the water and removes them from thesystem. It is in this unit that chemically precipitated TOC removaloccurs. The clarifier 28 may be one of several types including aninclined plate settler, a gravity clarifier, solids a contact clarifier,a sludge blanket clarifier, or a dissolved air flotation unit. Each typeof clarifier has benefits depending upon the quality of the raw watersource.

The water then flows from the clarifier 28 and is directed into asecondary mixing tank 30. The secondary mixing tank 30, like the primarymixing tank 14, may comprise a single mixing zone having a single mixer34, as shown in FIG. 1, or multiple mixing zones with multiple mixers22, 24 as shown in FIG. 2.

In the secondary mixing tank 30, the particulate charge of the water ismonitored and the appropriate amount of acid or base is added to thewater to maintain the optimum charge window in order to match theelectromagnetic charge of the membrane surface. The optimum chargewindow, which is typically in the low anionic (−) range, is chosen toalign with the natural surface charge of the membrane in order to reducefouling. Thus, the target electromagnetic charge may vary depending onthe type of filter used. Manufacturer of polymeric membrane filters mayutilize different membrane materials (e.g., Polyvinylidene Fluoride“PVDF”, poly ether sulfone “PES”, etc.), which can impart differingsurface charge characteristics. In addition, different manufacturingtechniques will undoubtedly produce membranes with different surfacecharge characteristics. Because the desired electromagnetic charge rangeis in the low anionic range, it is generally a base that is required tobe dosed. Dosing a base introduces anions into the water and affects theelectromagnetic charge of the particulates by making the charge moreanionic (−). Examples of bases that may be used are caustic soda or sodaash. The particulate electromagnetic charge can also be affected byfactors such as turbidity increase/decrease, temperature, conductivityand the type of particulates in the water.

For example, particulates in a water source will almost always carry ananionic charge. Thus, the higher the turbidity, the higher the overallcharge. In contrast, the addition of a coagulant will precipitate as aflocculated particle that carries a cationic charge. Higher or lowerdoses will offset against the naturally occurring anionic charges. Theresulting charge is, therefore, dependent upon the naturally occurringparticle charge and the “introduced” floc charge. Temperature can alsoalter particulate charges. As temperature decreases, overall anionicparticulate charge will decrease as well. However, a micro amp streamingcurrent monitor measures the charge of the flowing water streamregardless of turbidity, conductivity or temperature changes.

For example, in one embodiment the particulate charge of the water inthe secondary mixing tank 30 is preferably monitored by a micro ampstreaming current monitor 40, which displays the micro amp charge of theparticulates in the water. The electromagnetic charge of theparticulates may be monitored by other devices, such as a particlecharge analyzer or a zeta potential analyzer. Each device measures theparticulate electromagnetic charge by a different method and usesdifferent standards and units. For example, all specific numbers givenin this application refer to measurements taken by a micro amp streamingcurrent monitor made by the Milton Roy Company. The actual numbers willvary depending on the device used to measure electromagnetic charge.

The streaming current monitor 40 sends an electronic signal to themaster control panel 60, which determines the appropriate amount of acidor base to add to the water to maintain a charge of −9.8 to −9.4 microamps. It is understood that this charge reading can vary frommanufacturer to manufacturer and is dependent upon the methodcalibration. This optimum charge window is chosen to match theelectromagnetic charge of the membrane surface. The master control panel60 sends an electronic signal to the secondary acid/base dosing system32 to dose the appropriate amount of acid or base into the secondarymixing tank 30.

The water and acid or base is mixed in the secondary mixing tank 30.When the particulate charge of the water is stabilized, the water flowsfrom the secondary mixing tank 30 and passes through a low pressuremembrane filter 50. The membrane filter 50 removes particulates from thewater that are larger than the membrane's pore size, which is typically0.04-0.1 microns. The membrane filtration system provides the finalprocess step before the water is disinfected and distributed to homesand businesses. Though reference has only been made to a membranefilter, a conventional filter could also be used in accordance with thepresent invention.

A low pressure membrane filter operates by running in a feed pressuremode for pressure-based membrane filtration systems or a vacuum pressuremode for submerged or vacuum based membrane filtration systems. In thefeed pressure mode, the membrane filtration system passes water throughthe membrane under direct feed pressure. In the vacuum pressure mode,the membrane filtration system pulls water through the membrane undervacuum. The filtration runs may be set by time intervals (minutes offiltration) or the runs may be determined by pressure increase orfouling.

After the water passes through the membrane filter 50, the water isstored in a clear well 70. Chlorine is dosed into the water in the clearwell 70. Chlorine disinfectant is required to be introduced into a waterstream prior to the distribution system to prevent biological growth orcontamination of the filtered water supply. The system may furtherinclude a clear well level meter 66, which monitors the water in theclear well 70 and provides information to the master control panel 60via an electronic signal to determine the detention time of the water inthe distribution system. The detention time is important becausedisinfection byproduct (DBP) formation of regulated compounds such asHAA and THM occurs over time. The longer the detention time in thedistribution system, the greater the formation of these regulatedcompounds.

The system of the present invention depicted in FIG. 1, may furtherinclude means for controlling the amount of chlorine dosed into thewater in the clear well 70. For example, based upon the input signalsfrom the temperature sensor 44, the TOC analyzer 62, the UV 254 analyzer64 and the clear well level meter 66, the master control panel 60 maydetermine the amount of chlorine required to be dosed into the water inthe clear well 70. The master control panel 60 sends an electronicsignal to the chlorine dosing system 68 to dose the required amount ofchlorine.

The system of the present invention depicted in FIG. 1, may furtherinclude a protection system, wherein the pH of the water in thesecondary mixing tank 30 is monitored to ensure that the pH of the waterin the secondary mixing tank 30 is maintained within an optimum pHwindow.

For example, in accordance with the process and system of the presentinvention, the pH of the water in the secondary mixing tank 30 ismonitored by a pH probe 42. The pH probe 42 sends an electronic signalto the master control panel 60, which determines whether the pH of thewater is within the optimum pH window. If the pH of the water is outsideof the preset upper or lower pH values, which correspond to the optimumpH window, the master control panel 60 sends an electronic signal toshut off the primary and secondary acid/base dosing systems 18, 32 untila pH reading within the optimum pH window is received. Consistent withsuch a fail-safe system, an alarm may be triggered with the shut down ofthe coagulant, acid and base feed systems. In addition, the operatorwould typically check the entire system prior to manual restart of thesystem. The optimum electromagnetic charge and pH windows are dependenton the water source and the type of coagulant used. Generally, theoptimum pH window is in the range of about 7.0 to 8.0 standard units,but is dependent upon the characteristics of the water and coagulantused. The optimum electromagnetic charge window can also vary slightlydepending on the type of metal/salt coagulant used (e.g., aluminum oriron based).

The protection system may also include a mechanism for monitoring theperformance of the membrane filter 50. When the particulate charge or pHis outside of the optimum window for most efficient membraneperformance, membrane performance degrades immediately. For example, ifthe desired particulate charge for a given water stream is −9.7 microamps and the corresponding pH is 7.3, and it has been determined throughexperimentation that temperature variations that alter particulatecharge fall between a pH value of 7.1 and 7.4, a lower pH limit of 6.9and an upper pH limit of 7.6 can be incorporated into the mastercontrol. Should the pH measurement move outside of this preset range, itis an indication that there could possibly be a problem with the amountof chemical dosing. As a fail-safe measure, the system may trigger analarm and shut off the chemical feed.

The trans-membrane pressure (“TMP”), membrane resistance and membranepermeability may also be monitored at the membrane filter 50′ by amembrane performance sensor 46. The membrane performance sensor 46 sendsan electronic signal to the master control panel 60, which determines ifthe TMP, membrane resistance or the membrane permeability are within thepreset conditions. For example, if it has been determined that undernormal working conditions the system experiences an acceptable TMP riseof say 0.2 psi per day, a TMP rise rate that exceeds 0.5 psi per daywould trigger an alarm and shut off chemical feed as a fail-safemeasure. When the TMP, membrane resistance or membrane permeability isoutside of the preset conditions, the master control panel 60 shuts downthe secondary acid/base dosing system 32 until measurements within thepreset conditions are received.

Controlling the particulate charge and monitoring the pH, TMP, membraneresistance, and membrane permeability in the second stage of the processincreases the performance of the membrane filtration system.Specifically, advantages obtained are a higher membrane filtration rate,longer membrane filtration intervals, less membrane backwash waste andthereby water conservation, lower membrane chemical cleaningrequirements, and a longer membrane life.

With reference again to FIG. 2, a second embodiment of the membranefiltration system of the present invention will be described in greaterdetail. The embodiment of the membrane filtration system shown in FIG. 2comprises a single-stage or direct feed mode filtration process. Incontrast to the first embodiment, the direct feed mode does not includea clarifier element. In the direct feed mode, water bypasses theclarifier and proceeds directly to the membrane filtration system. Asdisclosed above in the paragraphs regarding the first stage of thetwo-stage process, the pH of the water can be lowered to as low as 4.5to 5.0 standard units to achieve the highest TOC removal. However, atthis pH and particulate charge level, if the water were to bypass theclarifier and be fed directly onto the membrane, the fouling rate of themembrane would increase dramatically. Therefore, in the direct feedmode, the pH and particulate charge of the water must be maintained atlevels that achieve as much TOC removal as possible while optimizingmembrane performance.

As shown in the FIG. 2 schematic diagram of the direct feed modeembodiment, a stream of raw untreated source water 10 is directed into amixing tank 14 where it is dosed with an effective amount of coagulantbased upon a variety of factors such as volume, TOC level andtemperature. The volume may be determined by means of a flow meter 12,which monitors the volume of source water 10 flowing into the mixingtank 14. The TOC level may be determined by means of a TOC analyzer 62and UV 254 analyzer 64 described previously. The temperature may bedetermined by means of a temperature sensor 44.

The particulate charge of the water in the mixing tank 14 is alsomonitored by means of a micro amp streaming current monitor 40. Thewater in the mixing tank 14 is then dosed with an appropriate amount ofacid or base to maintain the particulate charge of the water within theoptimum charge window for the membrane filter 50. Once theelectromagnetic charge of the water in mixing tank 14 is stabilized andthe coagulant is completely dispersed, the water passes through amembrane filter 50, which filters out the flocculates and insolubleparticulates from the water.

The system depicted in FIG. 2 may also include a protection system forpreventing runaway chemical dosing comprising a pH probe 42 to monitorthe pH of the water in the mixing tank 14 and a membrane performancesensor 46, which monitors the TMP, membrane resistance and membranepermeability of the membrane. Should any of the measurements be found tobe outside of preset values for pH, TMP, membrane resistance or membranepermeability is received, the system may be shut down until anacceptable measurement is received.

In a preferred embodiment of the filtration system depicted in FIG. 2,the system further includes a master control panel 60, which collectsand analyzes data inputs from the flow meter 12, TOC analyzer 62 and UV254 analyzer 64, to determine an effective amount of coagulant to beadded to the water in the mixing tank 14. Measurement data from the flowmeter 12, TOC analyzer 62 and UV 254 analyzer 64 are typically sent tothe master control panel 60 by means of wireless or hardwire electronicsignal communications. Based upon data input from the flow meter 12, thetemperature sensor 44, the TOC analyzer 62, and the UV 254 analyzer 64,the master control panel 60 uses a programmed algorithm to calculate aneffective amount of coagulant to be added to the water in the mixingtank 14.

For example, the flow meter 12 sends an electronic signal to a mastercontrol panel 60 regarding the volume of the water entering the mixingtank 14. The temperature sensor 44, TOC analyzer 62 and UV 254 analyzer64 monitor the water in the mixing tank 14 and send their measurementdata to the master control panel 60 via electronic signals. Based on thedata from the flow meter 12, the temperature sensor 44, the TOC analyzer62, and the UV 254 analyzer 64, the master control panel 60 uses aprogrammed algorithm to calculate an effective amount of coagulant to beadded to the water in the mixing tank 14. The master control panel 60then sends an electronic signal to coagulant dosing system 16, whichdoses an effective amount of coagulant into the mixing tank 14.

The master control panel 60 can also be used to monitor and maintain theparticulate charge of the water in the mixing tank 14 within the optimumcharge window. For example, the particulate charge of the water inmixing tank 14 is monitored by a micro amp streaming current monitor 40.The micro amp streaming current monitor 40 sends an electronic signal tothe master control panel 60, which calculates the appropriate amount ofacid or base to add to the water to maintain the particulate chargewithin the optimum charge window. The master control panel 60 sends anelectronic signal to the acid/base dosing system 18 to dose theappropriate amount of acid or base into the mixing tank 14.

The mixing tank 14 may comprise a single mixing zone with a single mixer20, as shown in FIG. 1, or preferably multiple mixing zones withmultiple mixers 22, 24, as shown in FIG. 2 to mix the water, coagulantand acid or based thoroughly. The mixers are preferably verticallymounted, propeller-type agitators. Referring to FIG. 2, when multiplemixing zones are utilized, the first zone typically contains a rapidmixer 22, which rapidly mixes the water to quickly disperse thecoagulant, and the second zone containing a slower speed flocculation ormaturation mixer 24, which promotes the flocculation of chemicallyprecipitated particulates. Once the electromagnetic charge of the waterin mixing tank 14 is stabilized and the coagulant is completelydispersed, the treated water is immediately directed through themembrane filter 50, which filters out the flocculates and insolubleparticulates from the water.

The master control panel 60 may also be used monitor the pH level of thewater as it proceeds through the system and membrane performance data toautomatically protect the filtration system from runaway chemicaldosing. For example, the master control panel 60 may monitor datameasurement via electronic signals from a pH probe 42, which measuresthe pH of the water in the primary mixing tank 14, and a membraneperformance sensor 46, which measures the TMP, membrane resistance andpermeability of the membrane. If a measurement outside of preset valuesfor pH, TMP, membrane resistance or membrane permeability is received,the master control panel 60 shuts off the acid/base dosing system 18until an acceptable measurement is received.

Following filtration by the membrane 50, the filtered water may bedirected to a clear well 70 for temporary storage. A clear well levelmeter 66 monitors the water in the clear well 70 and providesinformation on the detention time of the water in the distributionsystem. Based on the input data from the temperature sensor 44, the TOCanalyzer 62, the UV 254 analyzer 64, and the clear well level meter 66,the amount of chlorine needed may be calculated so that a chlorinedosing system 68 can dispense the necessary amount of chlorine into theclear well 70.

In a preferred embodiment, the master control panel 60 is used tomonitor, calculate and dispense the amount of chlorine into the clearwell 70 necessary to maintain safe drinking water. For example, theclear well level meter 66 monitors the water in the clear well 70 andprovides information on the detention time of the water in thedistribution system to the master control panel 60 by an electronicsignal. Based upon the input data from the temperature sensor 44, theTOC analyzer 62, the UV 254 analyzer 64, and the clear well level meter66, the master control panel 60 calculates the amount of chlorine neededand sends an electronic signal to the chlorine dosing system 68 to dosethe necessary amount of chlorine into the clear well 70.

With reference to the Figures, and particularly FIG. 3, the mastercontrol panel 60 automates the process of the present invention tocontrol the amounts of coagulant, acid or base and chlorine that aredosed during the filtration process. Based on the input data from theanalyzers throughout the process, the master control panel 60 calculatesthe actual coagulant dose required for TOC removal to maintaindisinfection byproduct formation of haloacetic acid (“HAA”) and trihalomethane (“THM”) below regulatory limits. The master control panel 60 mayalso determine whether pH adjustment in conjunction with coagulantdosing is required, calculate the acid or base dose necessary tomaintain particulate charge within the optimum charge window, andcalculate the actual chlorine or disinfectant required to maintain theregulated residual limits in the distribution system.

In one embodiment, the master control panel 60 comprises a receiver forreceiving electronic signals. The electronic signals are typically a4-20 mA signal, though other means of transmission are possible. Themaster control panel 60 receives signals from the flow meter 12, pHprobes 26, 42, temperature sensor 44, micro amp streaming currentmonitor 40, membrane performance sensor 46, TOC analyzer 62, UV 254analyzer 64 and clear well level meter 66. A chlorine residual analyzermay optionally provide input signals as well.

Based on the input data, the appropriate amounts of coagulant, acid orbase, and chlorine to be dosed are determined via mathematical formulaor algorithm programmed into the master control panel 60. Themathematical formula or algorithm is based upon laboratory simulationthat determines the TOC removal using varying coagulants (at varyingconcentrations) and varying pH levels. In addition, laboratorysimulation can also be performed that simulates the formation of DBP andmeasures HAA and TTHM formation over time at a certain temperature. Thistesting and simulation, as well as the TOC removal and DBP formation“on-site”, can provide the information necessary to enter into theformula/algorithm that the Master Control Panel uses to dose coagulant,set pH and dose chlorine. The master control panel's 60 transmitter thensends electronic signals to the coagulant dosing system 16, acid/basedosing systems 18, 32, and chlorine dosing system 68 to dose theappropriate amounts of the respective chemical into the water.

The master control panel 60 also protects against the possibility ofoverdosing acid or base in controlling pH and particulate charge.Default set points for pH, TMP, membrane resistance, and membranepermeability are stored in the master control panel 60. Whenmeasurements outside of these set points are received, the mastercontrol panel 60 is programmed to shut off acid and base dosing untilacceptable measurements within the set points are obtained. For example,if the optimum membrane performance window pH is between 7.2 and 7.5standard units, the master control panel 60 will not allow the pH dosingsystem to dose when the pH is measured outside of this window.

It will now be evident to those skilled in the art that there has beendescribed herein an improved membrane filtration system and process thatenhances total organic carbon removal while maintaining optimum membranefilter performance.

Although the invention hereof has been described by way of a preferredembodiment, it will be evident that other adaptations and modificationscan be employed without departing from the spirit and scope thereof. Forexample, the above described process for maximizing TOC removal andmembrane filtration performance could also include controlling otherconstituents in the water such as alkalinity adjustment, varying typesof dual stage chemical coagulants, and powered activated carbon (“PAC”)dosing. Other technologies can be added to the process such as IonExchange ahead of the process and Granular Activated Carbon Adsorptionafter the process or the process described may be a stand alone processfor drinking water filtration. The flexibility of the process allows fornewer types of liquids-solids clarifiers and newer, more advancedmembrane materials.

The above described invention discloses a system and process forenhancing TOC removal from raw, untreated water while maintainingoptimum membrane filter performance. Although the invention has beenparticularly shown and described, the disclosure is not intended tolimit the scope of the invention. The terms and expressions employedherein have been used as terms of description and not of limitation; andthus, there is no intent of excluding equivalents, but on the contraryit is intended to cover any and all equivalents that may be employedwithout departing from the spirit and scope of the invention. It will beunderstood by those skilled in the art that various changes in form andconditions may be made therein without departing from the spirit andscope of the invention.

I claim:
 1. A process for optimizing the removal of total organic carbon(TOC) from water while enhancing the performance of a membrane filter,comprising: monitoring a TOC level of said water; dispersing aneffective amount of a coagulant into said water based on the TOC level;monitoring a pH level of said water; and adjusting the pH level of saidwater, prior to said water being directed through said membrane filter,to align the particulate charge of said water with an electromagneticsurface charge of said membrane filter by measuring the particulatecharge of said water using a micro amp streaming current monitor anddosing said water with acid or base to maintain the particulate chargeof said water within an optimum charge window of between −9.8 and −9.4micro amps for said membrane filter.
 2. The process of claim 1, whereinsaid effective amount of coagulant is further based upon at least one ofa volume and temperature of said water.
 3. The process of claim 1,further comprising suppressing the pH of said water prior to saidcoagulant dispersing step.
 4. The process of claim 3, wherein saidsuppressing the pH of said water includes dosing said water with acid orbase to maintain a pH of 4.0 to 6.0 standard units.
 5. The process ofclaim 1, further comprising directing said water through a mechanicalclarifier device prior to said adjusting step, but after said coagulantdispersing step.
 6. The process of claim 2, wherein said effectiveamount of coagulant is further based upon the optimum charge window forsaid membrane filter.
 7. The process of claim 1, further comprisingmonitoring a trans-membrane pressure of said membrane filter andpreventing said water from being directed through said membrane filterwhen said trans-membrane pressure exceeds a predetermined value.
 8. Themethod of claim 1, wherein the coagulant is dispersed in a first stageand the particulate charge is aligned with the electromagnetic surfacecharge of said membrane filter in a second stage.
 9. The method of claim8, wherein a first pH level is maintained in the first stage to maximizeTOC removal during liquids-solids filtration, and wherein a second pHlevel is maintained in the second stage to optimize performance of saidmembrane filter.
 10. The method of claim 9, wherein the first pH levelis 4.0 to 6.0 and the second pH level is 7.0 to 8.0.
 11. The method ofclaim 9, wherein the first pH level is maintained upstream of aclarifier, and wherein the second pH level is maintained downstream ofthe clarifier and upstream of said membrane filter.
 12. The method ofclaim 1, wherein coagulant is dispersed and the pH level is adjusted ina single stage upstream of said membrane filter to achieve as much TOCremoval as possible while optimizing membrane performance.
 13. Themethod of claim 12, wherein said water bypasses a clarificationoperation.
 14. The method of claim 1, further comprising dosing chlorineto treated water downstream of said membrane filter.